1. Field of the Invention
The present invention relates to a computer system, and more particularly to a method and apparatus for supporting multiple display sessions through a single address on a non-programmable-terminal (NPT) attached to a host computer.
2. Description of the Prior Art
Known non-programmable, non-graphical, character-based terminals (NPTs), which attach to a host computer, such as an IBM AS/400, can support multiple display sessions and a single printer session simultaneously. Typically, the NPTs can display one or more display sessions at the same time using split screen formats that divide the physical screen between two or more sessions. Split screens allow the user to work in one session while monitoring the status of other sessions. Typically the NPTs are attached to the AS/400 via a twinaxial cable. The NPTs require the support of a workstation controller (WSC) for keystroke handling, screen/field management, and the like. Typically the WSC has seven available physical addresses for each multidrop, daisy-chained twinaxial cable port. In the known conventional arrangements, each NPT session requires a physical address. In order to support multiple display sessions on the NPT, an address is assigned to each session. If an NPT is supporting three display sessions and a printer session, for example, the NPT uses four addresses of the seven available addresses. As a result, two NPTs, each of which being configured as supporting three display sessions and a printer session, cannot be connected to the AS/400 through a single port. As the use of multiple sessions by customers increases, this restriction on the number of NPTs on a single port presents a problem.
Also, the total capacity of the WSC is reduced. For example, a WSC may support up to 40 sessions. This formerly meant that 40 physical devices were supported. However, with the NPT supporting four sessions, as few as ten physical devices can be supported. In order to support new devices, additional twinaxial cables and additional WSCs can be required.
Some programmable workstations (PWS) use the support of more than seven sessions on a single port by directly communicating with the host computer. However, this method cannot be used for an NPT since it requires a more powerful central processing unit (CPU) and much greater storage/memory capacity than the current NPTs accommodate. Supporting such a CPU and a large amount of storage/memory in the terminal not only makes it difficult to maintain but also results in the considerable price increase which is unacceptable for any NPT.
Important objects of the present invention are to provide a method and apparatus for supporting multiple display sessions through a single address on a non-programmable-terminal (NPT) attached to a host computer; to provide such method and apparatus substantially without negative effects; and to provide such method and apparatus that overcome many of the disadvantages of prior art arrangements.
In brief, the objects and advantages of the present invention are achieved by a method and apparatus for supporting multiple display sessions through a single address on a non-programmable-terminal (NPT) attached to a host computer by a work station controller (WSC). The WSC enables shared addressing of multiple display sessions on the NPT. The WSC changes focus to a selected one of the multiple display sessions responsive to receiving from the host computer a data stream for a requested display session not having the focus and responsive to receiving a change focus request from the NPT.